Screw elements for multi-shaft screw-type machines

Abstract

The invention relates to screw elements ( 10, 10 ′) for multi-shaft screw-type machines having screw shafts (W, W′) rotating pairwise in the same direction, wherein said screw elements scrape off one another precisely and the screw shafts composed of said screw elements have two or more screw flights. The screw profiles ( 11, 11 ′) can be represented over the entire cross section by respective profile curves, each profile curve ( 11, 11 ′) having at least one inflection point (K, K′) lying inside an outer radius (RA, RA′) of the profile curve over the progression thereof. The inflection point is considered to be a position of an abrupt change of pitch or a geometrical discontinuity in the pitch of the profile curve. The invention further relates to a method for producing screw elements ( 10, 10 ′), wherein circular arcs (1-5) are combined into a curve to form the screw profiles ( 11, 11 ′), the curve having at least one inflection point (K, K′) or one point of discontinuity in the pitch of the curve over the progression thereof, said point (K, K′) lying inside an outer radius (RA, RA′) of the profile curve. The invention additionally relates to screw-type machines having the screw elements according to the invention. The invention further relates to the use of screw elements according to the invention for extruding plastic materials.

1 .- 15 . (canceled) 
     
     
         16 . Screw elements ( 10 ,  10 ′) for multi-shaft screw machines with paired co-directionally rotating screw shafts (W, W′), these screw elements being fully wiping in pairs and screw shafts that are made up of these screw elements having two or more screw flights, the screw profiles ( 11 ,  11 ′) being able to be represented over the entire cross section by respective profile curves, characterized in that each profile curve ( 11 ,  11 ′) has at least one kink location (K, K′) along it that lies within an outer radius (RA, RA′) of the profile curve, the ratio of a radius of curvature of the screw profile to the outer radius of the profile being 0.05 to 0.95. 
     
     
         17 . The screw elements ( 10 ,  10 ′) as claimed in  claim 16 , each profile curve being a continuous, closed, convex curve, which is also continuously differentiable apart from the at least one kink location (K, K′). 
     
     
         18 . The screw elements ( 10 ,  10 ′) as claimed in  claim 17 , the profile ( 11 ) of the one screw element ( 10 ) being formed by a curve {right arrow over (p)} and the profile ( 11 ′) of the other screw element ( 10 ′) being formed from the curve {right arrow over (q)} according to the following relationship (1):
     {right arrow over (q)}={right arrow over (p)}+a·{right arrow over (n)} ( {right arrow over (p)} )+{right arrow over (α)}  (1),
 
 
       where
 the curve {right arrow over (p)} has at each point a radius of curvature p that is less than or equal to a centerline distance a between the screw elements ( 10 ,  10 ′), 
 for each point of the curve {right arrow over (p)} within a continuously differentiable portion there exists a normalized normal vector {right arrow over (n)}({right arrow over (p)}) with the length  1 , which at the respective point is perpendicular to the tangent to the curve {right arrow over (p)} and points in the direction of the center point of curvature belonging to the respective point of the curve {right arrow over (p)}, 
 {right arrow over (α)} is a vector which leads in the direction from the point of rotation (C) of the generating profile ( 11 ) to the point of rotation (C′) of the generated profile ( 11 ′) and has the length a. 
 
     
     
         19 . The screw elements ( 10 ,  10 ′) as claimed in  claim 16 , each screw profile or each profile curve ( 11 ,  11 ′) being made up of a number of arcs of a circle ( 1 - 5 ), the respective arcs ( 1 - 5 ) being at an angle (θ) of between 90° and 180°, preferably between 140° and 180°, to one another at the at least one kink location (K, K′). 
     
     
         20 . The screw elements ( 10 ,  10 ′) as claimed in  claim 16 , each screw profile or each profile curve ( 11 ,  11 ′) allowing itself to be subdivided into profile portions, which can be transferred into one another by point or axis mirroring. 
     
     
         21 . The screw elements ( 10 ,  10 ′) as claimed in  claim 20 , each profile portion being made up of a number of arcs of a circle ( 1 - 5 ), the number of arcs ( 1 - 5 ) that form one of the profile portions being preferably 2 to 8, particularly preferably 3 to 6. 
     
     
         22 . The screw elements ( 10 ,  10 ′) as claimed in  claim 20 , one of the profile portions extending between a point (PA, PA′), which lies on the outer radius (RA, RA′) of the profile ( 11 ,  11 ′), and a point (PI, PI′), which lies on the core radius (RI, RI′) of the profile ( 11 ,  11 ′), and comprising the at least one kink location (K, K′). 
     
     
         23 . The screw elements ( 10 ,  10 ′) as claimed in  claim 20 , each profile portion comprising a continuously differentiable curve between two kink locations (K, K′). 
     
     
         24 . The screw elements ( 10 ,  10 ′) as claimed in  claim 16 , the ratio of a radius of curvature of the screw profile to the outer radius of the profile being 0.2 to 0.8, preferably 0.3 to 0.7, particularly preferably 0.35 to 0.65, preferably at the point PA which cleans the barrel. 
     
     
         25 . A method for producing screw elements ( 10 ,  10 ′) for multi-shaft screw machines with paired co-directionally rotating screw shafts, these screw elements being fully wiping in pairs and screw shafts that are made up of these screw elements having two or more screw flights, for producing the screw profile ( 11 ,  11 ′) a profile curve being created in a plane perpendicular to the axis of rotation (C, C′), which profile curve has at least one kink location (K, K′) or a location of discontinuity in the slope of the curve along it, this location (K, K′) lying within an outer radius (RA, RA′) of the profile curve. 
     
     
         26 . A method for producing screw elements ( 10 ,  10 ′) for multi-shaft screw machines with paired co-directionally rotating screw shafts, these screw elements being fully wiping in pairs and screw shafts that are made up of these screw elements having two or more screw flights, characterized in that, in a first step for producing the screw profiles ( 11 ,  11 ′), a profile curve is created in a plane perpendicular to the axis of rotation (C, C′), which profile curve has at least one kink location (K, K′) or a location of discontinuity in the slope of the curve along it, this location (K, K′) lying within an outer radius (RA, RA′) of the profile curve, and in a second step clearances are introduced. 
     
     
         27 . The use of screw elements ( 10 ,  10 ′) as claimed in  claim 16  or produced as claimed in  claim 25  in a screw machine. 
     
     
         28 . The use as claimed in  claim 27 , the screw elements ( 10 ,  10 ′) cleaning in pairs with a constant gap over their entire circumference, or the screw elements ( 10 ,  10 ′) cleaning in pairs with a gap that is not constant over the entire circumference. 
     
     
         29 . A screw machine, in particular an extruder, with paired co-directionally rotating screw shafts (W, W′), the screw shafts having screw elements ( 10 ,  10 ′) as claimed in  claim 16  or produced as claimed in  claim 25 . 
     
     
         30 . A method for extruding plastic compositions, characterized in that screw elements as claimed in  claim 16  or produced as claimed in  claim 28  or a screw machine as claimed in  claim 29  are used.